AU710046B2

AU710046B2 - Flexible pipe in which the creep of a sealing liner into the reinforcement is restricted

Info

Publication number: AU710046B2
Application number: AU16067/97A
Authority: AU
Inventors: Joel Le Nouveau
Original assignee: Coflexip SA
Current assignee: Technip Energies France SAS
Priority date: 1996-02-02
Filing date: 1997-01-31
Publication date: 1999-09-09
Anticipated expiration: 2017-01-31
Also published as: FR2744511A1; EP0877888A1; AU1606797A; DK0877888T3; FR2744511B1; BR9707238A; EP0877888B1; WO1997028393A1; US6085798A

Description

WO 97/28393 PCT/FR97/00190 tendency of the internal sheath to penetrate or creep increases with time and/or the severe service conditions of the flexible pipe, for example when the fluid to be conveyed flows at high pressure (several hundreds of bar) and high temperature (above 100'C), a high s temperature generally reducing the rigidity of the internal sheath.

When the internal sheath gradually penetrates the said spaces, either cracks are produced which thus affect the sealing function of the sheath, or one or more local ruptures of the sheath may even occur, the consequence of such incidents being that fluid passes out of the sheath which no longer provides the required sealing.

Several solutions have been proposed and/or adopted in order to limit or in an attempt to prevent the creeping of the sheath into the spaces between coils of the pressure arch.

One solution, the simplest, consists in choosing a material and a great thickness for the sheath, so that it has better mechanical performance and higher chemical resistance. The drawback of this solution is twofold: it is more difficult to produce the flexible pipe because of the large size of the sheath and the cost of manufacture is very high.

Another solution consists in using a more precious material in order to keep the sheath to an acceptable thickness. Thus, instead of using a polyethylene to make the sheath, use has been made of a polyamide, the cost of which is very markedly higher than that of polyethylene.

Other solutions which in some cases are not directly related to the subject-matter of this invention are proposed and described in WO-A-82/01159, US-A-3,880,195, EP-A-0,166,385,

EP-A-

0,147,288, FR-A-2,465,416 and FR-A-2,417,707.

The prior art most closely related to the invention consists of documents US-A-3,729,028 and FR-A-85 17497.

In document US-A-3,729,028, the sealing internal sheath comprises a wound strip but neither the structure nor the mechanical properties of the strip, apart from the fact that it is of rectangular section, are described or even suggested.

WO 97/28393 PCT/FR97/00190 Document FR-A-85 17497, like the present invention, uses an intermediate strip capable of restricting the creeping of the internal sheath between the coils of the pressure armor layer for resisting the internal pressure. According to that document, the intermediate strip, which may be wound around the internal sheath in the direction of winding of the coils of the pressure armor layer or in the opposite direction, needs to have a high elastic modulus in the direction of winding. For that, and with the purpose of obtaining satisfactory results, it is recommended that use be made, for producing the tape, of substantially uni-directional fibres extending in the direction of winding and coated in a synthetic resin and preferably in a resin that is at least partially thermoplastic, which can possibly be fixed by bonding or melting. The transverse modulus of the strip is low so as to keep the pipe flexible. In the examples illustrated, the elastic modulus in the direction of winding has to be equal to at least 10,000 MPa, it being possible for the longitudinal fibres to be made of several E, R or S glass fibres, carbon fibres, silicon carbide, polyethylene with a high molecular mass, or aromatic polyamide.

However, no mention is made of the structure of the strip, except that it comprises longitudinal fibres with a high elastic modulus and that the strip is wound under low tension, for example of the order of daN.

But, only the longitudinal fibres offer resistance to the internal pressure, whereas no resistance is offered to the internal pressure between the longitudinal fibres. This being the case, the internal sheath tends to deform the intermediate strip and therefore to creep between the coils of the pressure armor layer and this is because of the low resistance offered by the transverse filaments. In order possibly to overcome such a drawback, it is therefore recommended that several intermediate strips be wound, superimposed on one another, and preferably wound alternately, something which not only increases the overall weight of the flexible pipe, but also prohibitively increases the cost of manufacture. In fact, it would be necessary to employ as many non-oxidizing flame torches as there are superimposed strips in order to bring about surface melting of the P:\OPER\AXD\2070909.RSI 6/7/99 -4polyethylene at the moment that each intermediate strip is brought into contact with the internal sheath on the one hand, and to use a greater number of carbon and aromatic-polyamide fibres, on the other hand. What is more, the constraints of winding with specific angles according to the envisaged application merely further increase the cost of manufacture, not to mention the other secondary products needed for manufacturing the intermediate strip, such as the coating for the longitudinal fibres in a resin to give them the required cohesion.

Advantageously, the present invention provides a flexible pipe provided with an intermediate strip which prevents the sealing internal sheath from creeping between the coils of the winding of the pressure armor layer.

According to the present invention, there is provided a flexible pipe that can be used for conveying fluids, of the type comprising at least a sealing internal sheath; an assembly of external armor layers for withstanding the physico-chemical stresses applied to said flexible pipe, said assembly comprising a pressure armor layer resistant to the pressure of the fluid to be conveyed, said pressureresistant armor layer consisting of non-contiguous coils wound around said internal sheath in a predetermined direction; an intermediate strip arranged between the pressure-resistant armor layer and the sealing internal sheath and wound around said sealing internal sheath in a direction parallel or opposite to the direction in which the coils of the pressure-resistant armor layer are wound, wherein the intermediate strip has a low elastic modulus in the direction of winding around said sealing internal *sheath and a high strength and elastic modulus in the direction transverse to said coil-winding direction.

One advantage of the present invention lies in the fact that the anti-creep intermediate strip strongly resists the internal pressure of the fluid, thus considerably restricting the penetration or creep of the material of which the sealing internal sheath is made and does so for the essential reason that only those points of the strip which have the greatest mechanical strength oppose the said internal pressure.

According to another feature, the strip consists of crossed longitudinal filaments and transverse filaments, the transverse filaments having an elastic modulus and a mechanical strength which are high. The strip is preferably of woven type and is dry in all cases, that is to say comprises no or practically no binding material other than what is necessary for manufacturing and manipulating it and conventionally used in the manufacture of such strips. Thus it is no longer necessary to envisage stages of rigidifying and/or fixing some of its components, as was the case with the intermediate strips ~7of the prior art.

WO 97/28393 PCT/FR97/00190 In addition, the filaments of which the strip is made are rovings, each roving comprising filaments in a number and of a nature that are appropriate for giving them the desired mechanical properties. In one embodiment of the strip, the transverse filaments s are inclined with respect to the longitudinal filaments by an angle of about 550 which is the angle of winding of the reinforcement filaments leading to a flexible pipe that is dimensionally stable under the effect of the internal pressure.

When the said weft filaments are wound at this equilibrium angle of approximately 550, the said filaments practically do not move at all and therefore do not rub on the liner or on the pressure armor layer.

Furthermore, as the weft filaments are transverse to the gaps between coils of the pressure armor layer, they form a short is "beam" which works in bending and effectively opposes the penetration of the internal sheath.

Other features and advantages will become clear from reading the description of several embodiments of the invention, and from the appended drawings in which: Figure 1 is a part view in perspective of a flexible pipe according to the invention.

Figure 2 is an example of a cross section of two noncontiguous coils of the pressure arch of the pipe depicted in Figure 1.

Figure 3 is a part view in plan of the intermediate strip according to a first embodiment.

Figure 4 is a very schematic and not-to-scale partial depiction of a longitudinal section through the pipe of Figure 1.

A flexible pipe of the smooth-bore type generally comprises, from the inside outwards, an internal sheath 1, of the polymeric type, a pressure armor layer or vault pressure 2, consisting of a winding of filaments of appropriate section, for example in the shape of a Z and called zeta-filament, as depicted in Figure 2 or alternatively in the shape of a U or T, a tensile armor layer 3 that resists the axial tension in the longitudinal direction of the flexible pipe, the said tensile armor layer customarily consisting of one or WO 97/28393 PCT/FR97/00190 more pairs of layers of winding 4,5 which are wound in opposite directions and inclined at an angle of less than 550, and an outer sealing sheath 6, of the polymeric type. In some applications, the various armor layer or winding layers are separated from one another by a textile layer, made of plastic of the same type as or of a different type from the outer sealing sheath 6.

The pressure armor layer 2 consists (Figure 3) of at least one winding in a direction e, with non-contiguous coils 7, 8 so that a space 9 is left between the two consecutive coils 7, 8. When the flexible pipe is pressurized by the fluid flowing at a relatively high temperature through the said pipe, the internal sheath 1 tends to deform and locally penetrate at the said spaces 9. Such penetration or creeping is depicted in Figure 2 by waviness 10 in the thickness of the liner 1. The progressive deformations of the internal sheath 1 into the spaces 9 lead to cracking and even to one or more local ruptures, causing a loss of sealing, and the extent to which this is observed is all the greater, the larger the spaces 9 and the larger the diameter of the pipe. These phenomena of cracking and/or weakening of the internal sheath are amplified in pipes said to be dynamic, as opposed to static pipes.

According to the present invention, an intermediate anticreep strip 11 is inserted between the internal sheath 1 and the pressure armor layer 2. The strip 11 may be wound in a first direction, approximately in the same direction e as the direction of winding of the pressure armor layer 2, but forming an angle u. of close to 900 and preferably between 80 and 850 with respect to the axis of symmetry AA' of the flexible pipe (Figure The strip 11 may also be wound in the opposite direction to the said first direction, with contiguous coils or overlapping coils.

The strip 11 consists (Figure 4) of crossed longitudinal warp filaments 12 and weft filaments 13 the direction e' of which is transverse to the direction e of winding of the coils 7,8, the strip 11 being produced with a loose weave. The warp filaments 12 have a low elastic modulus, compared with the weft filaments 13. By way of example, the elastic modulus of the warp filaments 12 is less than or WO 97/28393 PCT/FR97/00190 equal to 10,000 MPa, whereas the elastic modulus of the weft filaments is at least equal to 50,000 MPa. Likewise, the grammage of the warp filaments 12 and of the weft filaments 13 is respectively between 40 and 100 g/m 2 and between 100 and 300 g/m 2 which leads to a strip with a mechanical strength of between 100 and 300 daN/5 cm in the direction of the warp filaments 12, and in excess of 1000 daN/S cm in the direction of the weft filaments 13.

The loose weave of the strip 11 is produced in such a way that the pitch p between the warp filaments 12 is about 3 mm, i0 whereas the pitch p' between the weft filaments 13 is about 1 mm.

Quite obviously, other methods of manufacturing the strip 11, such as knitting, may be envisaged. The same applies to the respective orientations of the warp filaments and of the weft filaments. The strip 11 of Figure 4 comprises perfectly straight warp filaments 12 directed in the direction of winding of the strip and more or less perpendicular to the weft filaments 13. The strip 11 may also be produced in such a way that the weft filaments 13 are inclined, forming an angle of about 550 to the warp filaments 12.

As a preference, the warp filaments 12 are filamentary rovings made of polypropylene polyethylene, polyester, which are twisted, whereas the weft filaments 13 may also be filamentary rovings, not twisted, made of polyamide, carbon, titanium, etc., and the constituent monofilaments of which are distributed more uniformly between the weft filaments. A structure of this kind presents several advantages. The first is that it eliminates or reduces the holes in the strip 11, giving the latter a more uniform and compact appearance so that the internal pressure is exerted on weft filaments which are broad compared with the slender warp filaments. The second advantage is that it is possible, in extremis, to use just one thickness of intermediate strip 11.

When the strip 11 is being wound around the internal sheath 1, this can be done with contiguous coils or with overlapping coils, the degree of overlap being between 10% and 50%. Likewise, to obtain a better distribution of the internal pressure across the intermediate strip 11 and to eliminate the risk of pressure in the holes 8 in the said strip, it is preferable for two strips 11 to be superposed on one another, in the same direction or in opposite directions. This is all the more possible if the strip 11 according to the invention is of small thickness between 50 and 70/100 mm.

Note that the strip 11 according to the invention is wound dry when it is wound around the internal sheath even though a small amount of binding material is used to manufacture it, which binding material is needed for holding the warp filaments and weft filaments together temporarily during weaving for example.

As a preference, the width of the intermediate strip is at least greater than the spacing between coils of the pressure armor layer. Advantageously, and in a preferred embodiment, the width of the strip is equal to at least twice the said spacing.

I

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers or steps.

9. 9 *99 9 9.~ 99 9..

P:\OPER\AXD\2070909.RS1 6/7/99 -9- THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. Flexible pipe that can be used for conveying fluids, of the type comprising at least a sealing internal sheath; an assembly of external armor layers for withstanding the physico-chemical stresses applied to said flexible pipe, said assembly comprising a pressure armor layer resistant to the pressure of the fluid to be conveyed, said pressure-resistant armor layer consisting of non-contiguous coils wound around said internal sheath in a predetermined direction; an intermediate strip arranged between the pressure-resistant armor layer and the sealing internal sheath and wound around said sealing internal sheath in a direction parallel or opposite to the direction in which the coils of the pressure-resistant armor layer are wound, wherein the intermediate strip has a low elastic modulus in the direction of winding around said sealing internal sheath and a high strength and elastic modulus in the direction transverse to said coil-winding direction.

2. Flexible pipe according to claim 1, wherein the intermediate strip consists of crossed filaments some of which are longitudinal and arranged in the direction of winding of said strip, the transverse filaments having a high mechanical strength exceeding 1000 daN/cm.

o 3. Flexible pipe according to claim 2, wherein the intermediate strip is a woven strip in which the warp filaments are arranged in the direction of winding of said intermediate strip, and the weft filaments of which constitute the transverse filaments and are arranged in a direction which is transverse with respect to said direction of winding.

4. Flexible pipe according to claim 3, wherein the warp filaments consist of filamentary rovings, the elastic modulus of each filamentary roving being less than or equal to 10,000 MPa, and the grammage of which is between 50 and 100 g/m 2 5. Flexible pipe according to claim 3, wherein the weft filaments consist of filamentary rovings the elastic modulus of which is greater than or equal to 50,000 MPa, and the grammage of which is between 100 and 300 g/m 2 6. Flexible pipe according to any one of claims 3 to 5, wherein the rupture load of the intermediate strip in the direction of the warp filaments is between 100 and 300 daN/S cm.

7. Flexible pipe according to any one of claims 2 to 6, wherein the intermediate strip comprises more transverse filaments than longitudinal filaments.

Claims

8. Flexible pipe according to any one of claims 3 to 6, wherein each warp filament is a twisted filament.
9. Flexible pipe according to any one of claims 3 to 6, wherein the weft filaments are untwisted.
10. Flexible pipe according to any one of claims 1 to 9, wherein the intermediate strip is wound around the sealing liner in a helix and at an angle at most equal to 900, and preferably of between 80 and 85
11. Flexible pipe according to any one of claims 1 to 10, wherein the intermediate strip is wound with an overlap, the degree of overlapping being greater than 10% and preferably equal to
12. Flexible pipe according to any one of claims 3 to 6, 8 or 9, or any one of claims 7, 10 or 11 when dependent on claim 3, wherein the warp filaments are made of plastic such as polypropylene, polyethylene or polyester.
13. Flexible pipe according to any one of claims 3 to 6, 8 or 9, or any one of i 15 claims 7, 10, 11 or 12 when dependent on claim 3, wherein the weft filaments are chosen from materials including a polyamide, carbon, titanium.
14. Flexible pipe according to any one of the preceding claims, wherein the intermediate strip is wound around the sealing internal sheath in the opposite direction to the direction of winding of the coils. 20 15. Flexible pipe according to claim 2, wherein the intermediate strip comprises longitudinal warp filaments and weft filaments that are inclined by an angle of about 550 with respect to the warp filaments.
16. Flexible pipe according to any one of the preceding claims, comprising at least i two intermediate strips wound around the sealing internal sheath.
17. Flexible pipe according to claim 16, wherein the intermediate strips are wound in opposite directions.
18. Flexible pipe according to any one of the preceding claims, wherein the width of the intermediate strip is equal to at least twice the spacing between coils of the pressure armor layer next to the sealing internal sheath. P:\OPER\AXD\2070909.RS1 6/7/99 -11 I-
19. intermediate Flexible pipe according to any one of the preceding claims, wherein the strip is a knit. Flexible pipe substantially as hereinbefore described with reference to the drawings. DATED this 6th day of JULY, 1999 COFLEXIP by DAVIES COLLISON CAVE Patent Attorneys for the Applicant(s) a a a a a a a a a a a a a a. a a a a.. a a.. WO 97/28393 PCT/FR97/00190 ABSTRACT A flexible pipe including at least one sealing liner an assembly of external reinforcements for withstanding the physical and chemical stress to which the flexible pipe is exposed, which assembly particularly comprises a reinforcement resistant to the pressure of the fluid to be conveyed, and consisting of non- contiguous coils wound around the said sealing liner in a predetermined direction an intermediate strip (11) arranged between the pressure-resistant reinforcement and the sealing liner and wound around the said sealing liner in a direction parallel or opposite to the winding direction of the coil of the pressure- resistant reinforcement. The intermediate strip (11) has a low elastic modulus of stiffness in said winding direction around the sealing liner and a high strength and modulus of stiffness in said winding direction transverse to said coil winding direction. Figure 3.